1. Field of the Invention
The present invention relates to a method of feeding fine particulate matter in a continuous manner, e.g., to different kinds of manufacturing processes. In the context of the invention, the term particulate matter is used generally in reference to any bulk particulate material. In a great number of applications, the material is in granular or powderform, whereby its flowing qualities can be improved by fluidization, which is implemented through blowing air into the material.
A system based on the so-called loss-in-weight gravimetric weighing technique is used for the control of the feeding.
2. Discussion of Background Art
The use of loss-in-weight feeding for the above-mentioned purpose is known in the art from different applications. The control system is implemented using equipment in which an essential part is formed by material storage means suspended on weight transducers comprising a so-called weighing bin or bins whose weight can be measured at a desired instant of time. The material flow is passed from such a bin to a feeder constructed to cooperate intimately with said container and having its operation controlled by a measurement signal obtained from the loss-in-weight information of said weighing bin.
A problem herein arises from the refilling of the weighing bin. Continuous operation of the system presumes that the refilling must be performed simultaneously with the discharge of the weighing bin contents for feeding which causes disturbances to the control of the feeder. Consequently, the refill phase is desired to be most instant, and during this time of weight uncertainty, the control system is attempted to be run under different kinds of empirical or computational algorithms. However, said in-evitable uncertain period of weight control remains a persistent problem.
Various solutions have been proposed to this problem, one of them being described in published German patent application Ser. No. 37 42 229. The arrangement disclosed therein is based on a loss-in-weight type of feeder in which the material flow to the feeder is passed via two series-connected weighing bins. The scale of the first weighing bin in the series connection is adapted to monitor the weight changes of this bin only, while the scale of the latter bin monitors the weight changes of the overall system. As a rule, the weight signal of the latter bin scale as such is used in the feeder control except in situations when the first bin is being refilled. In this situation, the control signal is conditioned by subtracting the weight signal of the first scale from the weight signal of the latter scale. Superficially the system operation appears unproblematic notwithstanding its simplifying approaches that inevitably degrade the accuracy of the control. An essential simplification is therein that, during the replenishment transfer of the material from the first weighing bin to the latter, the amount of material dropping between the bins can be known only computationally, not being under control of either scale which gives rise to an uncertainty factor in the control system.
In the art is also known an arrangement in which two feeders with a loss-in-weight control system are connected in parallel. In this configuration the loss-in-weight feeders are refilled alternatingly. Material feed is performed using the feeder which is not in its refill phase. A control arrangement based on the above-described principle is disclosed, e.g., in U.S. Pat. No. 4,579,252. While this arrangement offers a reasonable accuracy of weight control, the overall accuracy is degraded by the weighing errors during the feeder starting phases. The equipment costs of the system are high.
According to the present invention, in the above-described kind of continuously operating feeder control method in which the control of the material flow is accomplished by gravimetric loss-in-weight measurement of the feed rate and the continuous feed rate is maintained by means of alternating replenishment flows performed under gravimetric material flow measurement, the accuracy of control has been improved by virtue of providing the replenishment and feed phases with weight measurement subsystems operating independently from each other, subjecting the material flow passing via the replenishment and feed phases to realtime weight measurement at least by one of said subsystems and performing the control of the feed rate based on the sum function of the replenishment loss-in-weight signal and the feed loss-in-weight signal.
Advantageously, said realtime continuation of the mate. rial flow during either the replenishment phase or the feed phase performed under weight control is accomplished by arranging the material flow between the replenishment and the feed units to occur as a gravitational plug flow in which the material is passed as a continuous flow from the replenishment unit to the feed unit.
Further advantageously, the feed continuity is assured by performing the replenishment of the feed unit in an alternating manner using a greater number than two of the parallel-operating intercontainer replenishment flows.